Compression-ignition engine fuel



Patented Nov. 4,1941

UNITED STATES PATENT OFFICE COMPRESSION-IGNITION ENGINE FUEL Raphael Rosen, Elizabeth, N. J., assignor to Standard Oil Development Company, a comeration of Delaware No Drawing.

Claims.

- This invention relates to an improvement in fuels for compression-ignition engines, and particularly to improvements in the ignition quality Application December 22, 1938, Serial No. 247,219

and lubricity of fuels to be employed in high agents have been beneficial for a properly timed injection and combustion of the fuels.

It is an object of this invention to improve compression-ignition engine fuels with respect to both their engine performance and their lubricating qualities by the addition of an ingredient capable of making both improvements.

Other more detailed objects of this invention will become apparent from the following description.

More recently, in the preparation of fuels suitable for the high speed Diesel type of compression-ignition engines which operate at about 1,000 revolutions per minute or -more, it has been found preferable to use fuels having relatively narrow and lower boiling ranges, and, in some instances, chemically refined to a high degree -since such fuels have better ignition qualities than the more viscous and unrefined hydrocarbon fuels, but unfortunately many of these fuels with superior'ignition qualities lack the desirable lubricating function. While some lubricating quality is desirable in the fuel to lessen the wear of parts which must necessarily be lubricated by the fuel, a more serious problem is to elimi-.

. nate fuel leakage around plungers and valves and dribbling from the atomizing or injecting nozzles, becausecorrection of these latter defects is is'very essential for properly timed burning of the fuel in the engine. In accordance with the present invention, these fuels are provided with an agent which corrects their lubricating deficiency and, moreover, enhances their ignition qualities.

of Diesel fuels may be determined appropriately by the method more recently recommended by the S. A. E. Volunteer Group for Compression Ignition Fuel Research and described in the S, A. E. Journal of June, 1936, page 225. This consists in matching the performance of a fuel to be tested with a reference fuel having a known cetane number, the cetane number being the percentage of normal cetane by volume in a blend with alpha methyl naphthalene. Normal cetane serves as a standard of high ignition quality hydrocarbon fuel for Diesel engines, because it has a very short ignition lag, and the ignition lag of the reference fuel, consisting of cetane and alpha methyl naphthalene, is shortened very nearly in proportion to the increase in percentage of cetane by volume in the blend. Hence, the cetane number assigned to any Diesel fuel corresponds to the volume percentage of cetane in the reference fuel having equalignition qualities. 4

The novel addition agents of this invention are characterized as organic phosphates or esters of phosphoric acid, and more particularly, those containing thioand alkyl group substituents. The addition to or solution in hydrocarbon fuels of this type of compound for imparting better ignition qualities and injection performance to the fuels constitutes a more specific object of this invention. Classes of compounds characterized as organic phosphates with proved essential properties for the objects of this invention are exemplified by the following general formula:

' (ROMPO in which a sulfur atom may be substituted for each oxygen atom and where -R represents.

organic groups containing hydrogen and carbon preferably combined as in an alkyl, alkaryl or aralkyl group, the alkyl group being such as a methyl or an ethyl group, but preferably propyl'," isopropyl, amyl, and such higher homologous groups, their'isomers and their olefinic or naphthenic analogues, the alkaryl or aralkyl group being such as a benzyl, cresyl, and analogous groups. The presence of inorganic substituents, such as halogens, nitrate groups, andactive metals in some ofthe organic groups, particularly the alkyl groups, may add to their effective- The ignition qualities and engine performance ness in accelerating ignition.

clans-{ 'm CsHn): tricresyl dithiophosphate 3. Trithiophosphates, for example, triamyl trithiophosphate,

4. Tetrathiophosphates, for example,

triamyl tetrathiophosphate (CsH11S)sP-=S tri-para-cresyl tetrathiophosphate (CH3.CH4S) 3P=S These phosphates and thiophosphates may be prepared by reacting alcohols or phenols containing the desired alkyl groups with a pentavalent phosphorus compound-capable of undergoing a condensation reaction with the alcohol or phenol to produce the desired ester. The phosphates may be produced by the action of phosphoric acid di'-, rectly on-the alcohol or phenol, or, if desired,

. phosphorus oxychloride or-phosphorus pentachloride may be substituted for phosphoric acid. The thiophosphates may be prepared by the reaction of phosphorus pentasulfide with the alcohol or phenol, or by condensation of ortho phrilislphoric acid with a mercaptan or thio alco 0 The phenols to be used according to the present invention are obtainable as by-products in the liquefaction of coal, from cracked petroleum oils, from tar acids, by hydroxylation of aromatichydrocarbons, and by alkylation of phenols.

/ While the phosphate esters, in general, have been found effective for increasing the oiliness of 'Diesel fuels without any impairment to the ignition qualities of the fuels, the alkyl group and sulfur-containing phosphate esters have been found to be superior in improvingthe lubrication and proper 'atomization under extremely high pressure and in eflectively increasing the igm'tion qualities of the fuel. The effectiveness of these compounds in raising the cetanenumber of a hydrocarbon fuel is illustrated by the following to other phosphate esters. Evidently. the sulfur and alkyl group constituents in the phosphate esters not only aid in increasing the lubricity of a as a gas oil fraction boiling within the range of v 400 F. to 700 F., regardless of whether such a fraction be obtained from a naphthenic base, paramnic base, or a mixed base crude 011. Since the new and preferred .types of addition agents are chiefly advantageous for increasing lubricity of a fuel. they may be employed most valuably with light gas oil cuts having A. P. I. gravities above and viscosities in the range of about 30 to Saybolt seconds-at 100 F., and particularly those which have been chemically refined for the removal of aromatic and asphaltic compounds. The narrow boiling range cuts having a 10% distillation between 475 F. and 580 F. and a 90% distillation point between 600 F. and 675 F., exhibit in common superior ignition qualities regardless of the crude source, provided their aniline miscibility points are substantially above 140 F., and to impart this property of aniline miscibility to the oil may require an amount of chemical refining which tends to remove oiline'ss components. To derive the full benefits of high ignition qualities from these improved narrow fractions, it is important to provide them with an agent which is highly effective for imparting the desired lubricity without detriment to their ignitabulated results from comparative tests on samples of an unmodified hydrocarbon fuel with samples of the same fuel modified by a smallamount of an added phosphate ester.

From pertinent data as-illustrated in the foregoing table, it may be seen that the alkyl group containing thiophosphates are definitely superior tion qualities, or better yet, with more highly effective agents such as the alkaryl thiophosphates, capable of enhancing their ignition qualities. When blended with agents of this type, these less viscous fuels are improved more than a gas oil fraction and can thus have cetane numbers of about 60 to 80. r

In preparing the improved fuels according to the present invention, the phosphate ester is added to the hydrocarbon fuel base in amounts varying generally from 0.1% up to about 5.0% by weight, or to the limit of their solubility in the oil, depending upon the type of fuel and addition agent employed aswell as the design of the compression-ignition engine in which the fuel is to be used. Small quantities of these novel addition agents may be used for adapting various mixtures of hydrocarbons for use .as Diesel fuels including recycle stock from a cracking operation, nonparafllnic extracts, oils from destructive distillations, pyrobituminous and asphaltic materials and mixtures of these with one another or straight run petroleum fractions.

Other agentsfor enhancing various other physical and chemical characteristics of the fuel without detracting from the ignition quality of the fuel may be admixed, such as sludge dis-,

persers, dyes, corrosion inhibitors, anti oxidants,

viscosity improvers; pour point depressants, and gum solvents. Also, other promoters of ignition qualities may be admixed.

It is not intended that this invention be limited to the specific examples which were give merely for the sake of illustration. It is desired to claim all the novelty inherent in the invention in the appended claims as broadly as the prior art permits.

I claim:

1. A fuel composition for compression-ignition engines of the Diesel type comprising a hydrocarbon Diesel fuel blended with a thiophosphate ester containing in the molecule three to four sulfur atoms and three organic groups each of which has an alkyl group, the hydrocarbon components of said fuel composition boiling below 700 F. and said ester being added in sufllcient amount to substantially enhance the ignition quality of said fuel.

2. A fuel composition according to claim 1, in which said thiophosphate ester is a trialkaryl tetrathiophosphate.

3. A fuel composition according to claim 1 in which said thiophosphate ester is triparacresyl tetrathiophosphate. 

